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Vol. IV — Electronics · Tool

Reactance

Frequency turns a capacitor or inductor into an AC resistance. Change f and C or L — X updates as you type. Add series R for impedance magnitude and phase.

How it works

Reactance is how strongly a capacitor or inductor pushes back against AC. For a capacitor, Xc = 1 / (2πfC) — higher frequency or bigger C means less opposition. For an inductor, Xl = 2πfL — higher frequency or bigger L means more opposition.

With a series resistor R, the impedance magnitude is |Z| = √(R² + X²). Phase is φ = atan(X / R): capacitive X is negative (current leads voltage), inductive X is positive (current lags). Ideal L and C have no real resistance of their own; real parts add a little R.

Pair this with RC time for the timing side of the same parts, or pick resistors on Resistor codes. Back to the electronics bench.